This paper discusses the real-time aspects of networked control systems' (NCSs) operating environments. An open-loop unstable magnetic-levitation (Maglev) test bed was constructed and used to develop an NCS with a real-time application interface (RTAI) operating environment. A client-server architecture on a local area network (LAN) was developed with the network communication based on the user datagram protocol (UDP). The implementation of an event-driven server and a time-driven client presented in this paper facilitates a simple timing scheme that does not require clock synchronization between the client and the server. A novel prediction scheme involving the multiple-step-ahead generation of control signals is used to maintain system stability in the presence of excessive time delays and packet losses in the communication network. The current system can compensate for up to 20% data-packet losses without losing stability with the Maglev real-time-control test bed in the communication network.

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Real-time operating environment for networked control systems

This paper describes a new lecture/laboratory course being developed at The University of Michigan to provide students with technical knowledge and experience in incorporating computing elements into engineering designs and control systems. The course, intended for students with minimal computer background (e.g. one higher level language course), seeks to expose students to: the significance of various computer architectures to real time operations; software considerations to real time applications; interrupts and device handling; A/D and D/A conversation techniques; computer to computer communication; and an introducation to digital process control. A laboratory, composed of three LSI-11 microcomputer systems and hardware necessary to connect these to external devices, provides students with hands-on experience in the application of these topics. Laboratory emphasis is on use of computers as elements in control systems.

T. Boardman

Papers

A real time computer systems course for engineers